All bonds issued by the authority shall be signed by the chairman of its board or other chief executive officer and attested by its secretary, and the seal of the authority shall be affixed thereto, and any interest coupons applicable to the bonds of the authority shall be signed by the chairman of its board or other chief executive officer; provided, that a facsimile of the signature of one, but not both, of said officers may be printed or otherwise reproduced on any such bonds in lieu of his manually signing the same, a facsimile of the seal of the authority may be printed or otherwise reproduced on any such bonds in lieu of being manually affixed thereto, and a facsimile of the signature of the chairman of its board or other chief executive officer may be printed or otherwise reproduced on any such interest coupons in lieu of his manually signing the same. Any such bonds may be executed and delivered by the authority at any time and from time to time, shall be in such form and denominations and of such tenor and maturities, shall contain such provisions not inconsistent with the provisions of this chapter, and shall bear such rate or rates of interest, payable and evidenced in such manner, as may be provided by resolution of its board. Bonds of the authority may be sold at either public or private sale in such manner and at such price or prices and at such time or times as may be determined by the board to be most advantageous. The principal of and interest on any bonds issued or obligations assumed by the authority may thereafter at any time (whether before, at or after maturity of any such principal and whether at, after or not exceeding six months prior to the maturity of any such interest) and from time to time be refunded by the issuance of refunding bonds of the authority, which may be sold by the authority at public or private sale at such price or prices as may be determined by its board to be most advantageous, or which may be exchanged for the bonds or other obligations to be refunded. The authority may pay all expenses, premiums and commissions which its board may deem necessary and advantageous in connection with any financing done by it. All bonds issued by the authority shall be construed to be negotiable instruments although payable solely from a specified source. All obligations created or assumed and all bonds issued or assumed by the authority shall be solely and exclusively an obligation of the authority and shall not create an obligation or debt of any county or municipality; provided, that the provisions of this sentence shall not be construed to release the original obligor from liability on any bond or other obligation assumed by the authority. Any bonds issued by the authority shall be limited or special obligations of the authority payable solely out of the revenues of the authority specified in the proceedings authorizing those bonds. Any such proceedings may provide that the bonds therein authorized shall be payable solely from that one or combination of the following sources as may be set forth in any resolution of the board authorizing the issuance of such bonds: (a) any tax proceeds appropriated, allocated or made payable (in whole or in part) to such authority by or pursuant to any act of the legislature of the state or by or pursuant to any ordinance, resolution or order of the county in which the authority is authorized to furnish public transportation service or any municipality located in such county, and (b) the revenues derived from the operation of all transit systems owned by the authority or solely out of the revenues from the operation of any one or more of such systems or parts thereof, regardless of the fact that those bonds may have been issued with respect to or for the benefit of only certain particular systems of the authority. The authority may pledge for the payment of any of its bonds the revenues from which such bonds are payable, and may execute and deliver a trust indenture evidencing any such pledge or a mortgage and deed of trust conveying as security for such bonds the transit systems, or any part of any thereof, the revenues or any part of the revenues from which are so pledged. Any mortgage and deed of trust or trust indenture made by the authority may contain such agreements as the board may deem advisable respecting the operation and maintenance of the property and the use of the revenues subject to such mortgage and deed of trust or affected by such trust indenture, and respecting the rights, duties and remedies of the parties to any such instrument and the parties for the benefit of whom such instrument is made; provided, that no such instrument shall be subject to foreclosure.